Products of aluminum alloy prepared by powder metallurgy process (hereinafter referred to as "P/M process") exhibit highly improved heat resistance, wear resistance, and like properties in comparison with the products prepared by ingot metallurgy process (hereinafter referred to as "IM process") because the products by P/M process can contain additional elements in larger amounts with no segregation and much more uniformly dispersed in aluminum matrix than the products prepared by IM process.
Conventional P/M aluminum alloy products are usually produced by extruding a powdery, flaky or ribbon-like material to obtain a billet and processing the billet to the desired shapes or forms. During the hot extrusion step, the oxide films on the surfaces of powder particles, flakes or ribbons are fractured and the exposed inner aluminum portions are pressed each other to form strong bonding. In powder-rolling process and powder-forging process which also belong to a general category of P/M process, aluminum oxide films are fractured; however, since shearing force is relatively small and deformation of each particle is not so large and uniform as in the case of extrusion, the bond between particles is not so strong as in the extruded product.
The extrusion ratio in conducting the above extrusion by P/M process is usually 10 or more, preferably 20 or more to obtain a strong bonding of each particle. The extrusion by P/M process usually requires much higher forces than the extrusion by IM process because the aluminum alloy used in the former process contain larger amounts of alloying elements. For these limitations, aluminum alloy materials obtained by P/M process are difficult to employ for producing large-sized products.